1. Field of the Invention
This invention generally relates to a derivatized poly(ester amide) composition useful for coating an implantable device such as a drug delivery stent.
2. Description of the Background
Blood vessel occlusions are commonly treated by mechanically enhancing blood flow in the affected vessels, such as by employing a stent. Stents act as scaffoldings, functioning to physically hold open and, if desired, to expand the wall of the passageway. Typically stents are capable of being compressed, so that they can be inserted through small lumens via catheters, and then expanded to a larger diameter once they are at the desired location.
Stents are used not only for mechanical intervention but also as vehicles for providing biological therapy. Biological therapy can be achieved by medicating the stents. Medicated stents provide for the local administration of a therapeutic substance at the diseased site. Local delivery of a therapeutic substance is a preferred method of treatment because the substance is concentrated at a specific site and thus smaller total levels of medication can be administered in comparison to systemic dosages that often produce adverse or even toxic side effects for the patient. One method of medicating a stent involves the use of a polymeric carrier coated onto the surface of the stent. A composition including a solvent, a polymer dissolved in the solvent, and a therapeutic substance dispersed in the blend is applied to the stent by immersing the stent in the composition or by spraying the composition onto the stent. The solvent is allowed to evaporate, leaving on the stent surfaces a coating of the polymer and the therapeutic substance impregnated in the polymer.
Generally, a polymer forming a coating composition for an implantable device has to be biologically benign. The polymer is preferably biocompatible and bioabsorbable. One such polymer is poly(ester amide). Poly(ester amide) (PEA) has excellent biocompatibility. However, a coating formed of PEA can incur mechanical failures. In addition, PEA is more permeable to a drug such as everolimus than ethylene vinyl (EVAL) alcohol copolymer and polyvinylidene fluoride (Solef™). In order to achieve a proper level of residence time of an agent in a coated stent, it would require thicker coatings to meet release rate targets.
Therefore, there is a need for a PEA coating composition that provides for a controlled release of a bioactive agent and improved mechanical properties.
The compositions and the coatings formed thereof disclosed herein address the above described problems and needs.